How much muscle strength is required to walk in a crouch gait?

Abstract

Muscle weakness is commonly cited as a cause of crouch gait in individuals with cerebral palsy; however, outcomes after strength training are variable and mechanisms by which muscle weakness may contribute to crouch gait are unclear. Understanding how much muscle strength is required to walk in a crouch gait compared to an unimpaired gait may provide insight into how muscle weakness contributes to crouch gait and assist in the design of strength training programs. The goal of this study was to examine how much muscle groups could be weakened before crouch gait becomes impossible. To investigate this question, we first created muscle-driven simulations of gait for three typically developing children and six children with cerebral palsy who walked with varying degrees of crouch severity. We then simulated muscle weakness by systematically reducing the maximum isometric force of each muscle group until the simulation could no longer reproduce each subject's gait. This analysis indicated that moderate crouch gait required significantly more knee extensor strength than unimpaired gait. In contrast, moderate crouch gait required significantly less hip abductor strength than unimpaired gait, and mild crouch gait required significantly less ankle plantarflexor strength than unimpaired gait. The reduced strength required from the hip abductors and ankle plantarflexors during crouch gait suggests that weakness of these muscle groups may contribute to crouch gait and that these muscle groups are potential targets for strength training.

Figure 1

Musculoskeletal models used to create dynamic simulations of gait for individuals that walked in an unimpaired gait pattern (left) and individuals with cerebral palsy who walked in mild (center) and moderate (right) crouch gait.

Figure 2

The average hip, knee, and ankle kinematics (A) and kinetics (B) during unimpaired gait (dotted) and mild (light gray) and moderate (dark gray) crouch gait. Joint moments are normalized by body mass (kg).

Figure 3

Required strength for each muscle group that was necessary to recreate the subjects’ gait patterns expressed as percent of the maximum isometric force (average ± 1 SE, * p < 0.05 from Fisher’s Least Significant Difference test). The Fisher’s Least Significant Difference test was only performed if the p-value from the one-way ANOVA was less than 0.1. The ANOVA p-values for the hip abductors, quadriceps, and ankle plantarflexors were 0.05, 0.04, and 0.09, respectively.

Figure 4

Kinematics (A) and kinetics (B) for hip abduction and ankle plantarflexion for unimpaired children (N=82, dotted black) and individuals with cerebral palsy who walked in mild (N = 976, light gray) and moderate (N=209, dark gray) crouch gait who visited Gillette Children’s Specialty Healthcare. The peak hip abductor moment and ankle plantarflexor moment are smaller during mild and moderate crouch gait compared to unimpaired gait (ANOVA, p < 0.001). Joint moments are normalized by body mass (kg).